Pieces of fetal rat hippocampus transplanted to the anterior chamber of the eye became vascularized from the host iris and proliferate markedly, developing an adult organization in oculo. Cytological and electrophysiological studies revealed the development of the various strata normally associated with the adult hippocampus. Furthermore these studies revealed a marked chemo-sensitivity of pyramidal cells to acetylcholine via a muscarinic receptor, suggesting that normal pharmacological and cytological development of the hippocampus proceeds in the absence of extra-hippocampal afferents. In addition, the in oculo hippocampus develops a marked propensity for epileptogenic activity, much like that reported in situ. BIBLIOGRAPHIC REFERENCES: Lars Olson, Robert Freedman, Ake Seiger and Barry Hoffer, Electrophysiology and Cytology of Hippocampal Formation Transplants in the Anterior Chamber of Eye. I. Intrinsic Organization. Brain Research, 119: 87-106, 1977. B. Hoffer, A. Seiger, R. Freedman, L. Olson, and D. Taylor, Electrophysiology and Cytology of Hippocampal Formation Transplants in the Anterior Chamber of the Eye. II. Cholinergic Mechanisms, Brain Research, 119: 107-132. 1977.